<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <input type="text" name="" id=""> <button>点击</button>
    <script>
        var btn = document.querySelector('button')
        var i = 3;
        btn.addEventListener('click',function(){
            btn.disabled = true
           
            var st = setInterval(function(){
               
                  if(i==0){
                      clearInterval(st)
                      btn.disabled = false
                      btn.innerHTML = '点击'
                      i = 3;
                  } 
                  else {
                    btn.innerHTML = i
                  i--;
                  }
            },1000)
        })
      function f(){
            console.log(this);
            
        }
        var f1 = new f();
        // f1();
        
    </script>
</body>
</html>